Continuous esterification process



Aug. 21, 1956 W. E. CASH ET AL CONTINUOUS ESTERIFICAT ION PROCESS Filed Feb. 19, 1953 EsrEe/Frnvc IPEACTA/VTS E urea "vs/e G 2 Sheets-Sheet l I H ENTRA INEE AND VAPaQ:

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2,759,967 CONTINUOUS ESTERIFICATION PROCESS Wilfrid Ernest Cash, Chearn, and William Henry Gel], Hull, England, assignors to The Distillers Company Limited, Edinburgh, Scotland, a British company Application February 19, 1953, Serial No. 337,838

Claims priority, application Great Britain February 23, 1952 4 Claims. (Cl. 260-475) The present invention relates to the esterification of monohydric alcohols with acids and has whereby such tinuously to give an ester of very low tent.

The invention, accordingly,

organic acid concomprises the novel procspecific embodiments of hereinafter by way of example and in accordance with which We now prefer to practise the invention.

mentioned mvonohydric alcohol.

Among the carboxylic acids and anhydrides which can be esterified by the process of this invention may be acid, phthalic anhydride, sebacic acid,

ethylene glycol, diethylene glycol and glycerol. esters, such as the mono-esters of any of the above-mentioned dicarboxylic acids may be esterified in the way, and it is frequently convenient, when dealing with and then lead the solution of monoester in alcohol In the production of mixed esters, an acid ester of a different alcohol may be esterified in this Way.

The esterification catalyst employed may be of the conventional type, and sulphuric acid is preferred, suitable and particularly 01-05% The entrainer employed to remove the water or alcohol from the esterification or alcoholysis mixture respectively,

undergoing reaction. Thus, in the production by esterification of lower alkyl esters including butyl esters, it is lice to use a separate entrainer such as an aromatic hydrocarbon of 6-8 carbon atoms, for example benzene. The spent entrainer vapour may be treated separately so that the entrainer can be recycled.

However, lar entra mng agent employed does not diiference.

ing coil or other suitable heating means located in the liquid so that th controlled ber of sections to be used; for instance any number above three, such as five or In Figure l, the column A has eight plates Steam heating coils C1, C from a manifold and independently conout the apparatus may be checked. Thermometers (not shown) are also provided in each section.

Where the mixture to be esterified comprises a high boiling acid or anhydride, for example phthalic anhydride, the entrainer will merely collect the water liberated in the reaction. Entrainer and water vapour are then led to a separate decanter or fractionating column, depending on Whether the entrainer is immiscible with Water or not, and dry entrainer is returned to the base of the esterification apparatus. Where the mixture to be esterified, on the other hand, comprises a more volatile acid such as acetic acid, the entrainer will remove this component together with the water. In such a case, the entrainer and entrained vapours are led to a fractionating column where water is taken off overhead while the entrainer and acid are returned to the base of the apparatus.

The upper limit to the number of sections or vessels is not critical and is principally a matter of convenience, there being no particular advantage in employing, say, 50 such sections instead of if the contact time is maintained the same. Also, it is obviously not always essential to have all the sections heated. Moreover, the process may be operated with only partial counter-current flow of entrainer, the bottom two or three sections, say, being supplied independently with fresh dry entrainer, and the combined vapours from these sections led to the third or fourth section respectively for subsequent countercurrent flow to the head of the apparatus.

One of the advantages of the process of the present invention is the economy of entrainer secured by using it in countercurrent flow to the reactants, while the yield and quantity of ester produced remain at the same high level. If required, the advantages of countercurrent flow of the alcoholic component to the other reactant may be secured by adding more of the former to the later zones, thereby ensuring a minimum of organic acid in the product. Thus the reaction may be commenced with an excess of the organic acid, and the alcohol added during the progress of the reaction mixture through the successive zones until a slight or considerable excess is present in the efiluent, though an excess of the alcohol throughout the system may be maintained if desired. A further advantage in the process of the invention arises from the independent temperature control of each esterification zone. Only in this way is it possible to maintain the temperature in each zone at or near the optimum, a factor which is extremely important when it is borne in mind that in many of these esterifications a fall of only C. will result in the reaction velocity being halved.

The following examples illustrate the production of esters according to this invention, employing the apparatus of the type shown in Figure 1.

Example 1.--Di(2-ethylhexyl) phthalate The esterification unit consisted of eight sections above a base section, i. e., eight bubble cap plates. The liquid volume in each section was 3.75 gallons.

A feed mixture was prepared from phthalic anhydride and ethyl hexanol in a molar ratio of 1:2.75 and sulphuric acid was added to give 0.15% on the feed mixture. This mixture was fed into the top of the column, while benzene as entrainer, at the rate of 9 gallons per hour, was introduced at the bottom. The organic acidity of the liquid on the section immediately above the base section was determined, when conditions were stable, as 0.2% as phthalic acid. The water-benzene vapour was removed from the head of the column, condensed and passed to a separator, whence the benzene was returned to the bottom of the column.

Further details of the run are given in the following table and show the advantages in throughput per unit reaction volume and in benzene circulation per unit of the product.

Reaction volume, gallons 30 Monoester/alcohol feed, G. P. H 17 Per cent w./w. monoester in feed (app.) 40

Residence time, hours 1.7 Average reaction temperature, C Lbs. di-(Z-ethyl-hexyl) phthalate produced/ gallon reaction volume/hr 3.7 Lbs. of benzene circulated per lb. of di-(Z-ethylhexyl) phthalate produced 0.7 Organic acidity of product as per cent w./w. of

phthalic acid on di-(Z-ethyl-hexyl) phthalate 0.3 Per cent of phthalic anhydride esterified to diester 98.7

Lbs. of ethyl hexanol per lb. of di-(2-ethyl-hexyl) phthalate in product 0.25

In the above procedure the average reaction temperature in the reaction mixture was maintained at approximately 150 C. throughout the esterification apparatus by adjusting the amount of heat supplied to each section. By way of contrast the procedure was repeated in the same apparatus but heat was only supplied to the base and top sections of the esterification unit. In this way the incoming feed at the top of the unit was at 150 C. in the top section of the column and similarly the contents of the base section of the unit were also maintained at 150 C. In spite of the fact that the whole unit was well lagged against heat losses, the temperature of the reaction mixture in the intervening sections of the esterification unit dropped due to the heat absorbed in the vaporisation of the water formed in the esterification reaction. When the reaction is carried out in this way the total conversion to ester falls when the throughput in the unit is maintained at the same level as in the example proper.

Example 2.-Di-(2-ethyl-hexyl) phthalate A feed mixture was prepared from phthalic anhydride and 2-ethyl hexanol in the molar ratio of approximately 1:3, and sulphuric acid was added to give 0.10 to 0.15% by weight on the feed mixture. This mixture was fed continuously into the top plate of the reaction column, which had eight plates and a base section into which latter benzene vapour was introduced continuously as entrainer. The temperature of the liquid in the plates and base section was maintained at 150 C.

The water-benzene vapour was removed from the head of the reaction column, condensed and passed to a separator from which the benzene was returned to the base of the reaction column after passing down a conventional fractionating column which served to remove final traces of water from the benzene.

The liquid volume in each plate section was 3.75 gallons and in the base section 12.3 gallons.

The organic acidity of the liquid in the base section was determined, when conditions were stable, as 0.13% as phthalic acid.

Details of the run are as follows:

Reaction volume, gallons 42.3 Monoester/ alcohol feed, G. P. H 18.6 Per cent w./w. monoester in feed 43.5

Residence time, hours 2.27 Average reaction temperature, C 150 Lbs. di-(Z-ethyl-hexyl) phthalate produced/ gal. reaction volume/ hr Lbs. of benzene circulated/ lb. of di-(Z-ethyl-hexyl) phthalate produced Organic acidity of product as per cent w./w. of

phthalic acid on di-(Z-ethyl-hexyl) phthalate 0.17 Per cent of phthalic anhydride esterified to diester 99.2 Lbs. of 2-ethy1 hexanol per lb. of di-(Z-ethyl-hexyl) phthalate in product 0.33

Example 3.-Di-butyl phthalate Feed: Anhydride plus alcohol in molar ratio of 1:3, plus catalyst (up to 0.15% by weight on reactants).

Reaction column as in Example 2.

Entrainer: Butyl alcohol.

was returned to the base of the reaction column.

The organic acidity of the product was determined on the liquid in the base section.

RunNo 1 2 Reaction volume, gallons Monoester/alcohol feed, G. P. H Percent w./w. monoester in feed- Residence time, hours Average reaction temperature, Lbs. di-butyl phtha ate produced/gal.

ume r Lbis. 0133111331101 circulated/lb. of dibutyl phthalate prouce Organic acidity of product as percent w./w. of phthalic acid on dibutyl phthalate Percent of ph thalic anh ydride esterified to diester Lbs. oi butanol/lb. of dibutyl phthalate in product.-.

Example 4.Dimethyl phthalate column was rejected.

The organic acidity was determined on the liquid in the lowest plate in the reaction column (i. e. the plate immediately above the base section).

Reaction volume, gallons Monoester/alcohol feed, G. P. H '13 Per cent w./w. monoester in feed 60 Residence time, hours 2.3 Average reaction temperature, C 150 Lbs. dimethyl phthalate produced/gal. reaction volume/hour 3 4 Lbs. of methanol circulated/lb. of dimethyl phthalate produced 0.75 Organic acidity of product as per cent w./w. of

phthalic acid on dimethyl phthalate Per cent of phthalic anhydride esterifiedtodiester: 98.8 Lbs. of methanol/lb. of dimethyl phthalate in product 0.02

We claim: 1. A process for the production of a non-volatile ester which comprises passing a liquid reaction mixture of an alcohol and an organic reagent selected from the group an esterification catalyst concurrently through a series of at least three consecutive zones, said zones each being with separate heating means and being maintained at about C., passing vaporized entrainer is introduced.

3. A process for the which and a and being butanol as entrainer countercurrently through the mix- 4. A process for the production of di-(Z-ethyl-hexyl) phthalate which comprises forming a mixture of phthalic References Cited in the file of this patent UNITED STATES PATENTS 2,644,009 Cash et a1. June 30, 1953 

1. A PROCESS FOR THE PRODUCTION OF A NON-VOLATILE ESTER WHICH COMPRISES PASSING A LIQUID REACTION MIXTURE OF AN ALCOHOL AND AN ORGANIC REAGENT SELECTED FROM THE GROUP CONSISTING OF CARBOXYLIC ACIDS, CARBOXYLIC ACID ANHYDRIDES, CARBOXYLIC ACID ESTERS AND NEUTRAL CARBOXYLIC ACID ESTERS OF RELATIVELY VOLATILE ALCOHOLS, TOGETHER WITH AN ESTERIFICATION CATALYST CONCURRENTLY THROUGH A SERIES OF AT LEAST THREE CONSECUTIVE ZONES, SAID ZONES EACH BEING PROVIDED WITH INDEPENDENT HEATING MEANS AND BEING MAINTAINED AT SUCH TEMPERATURES THAT FRACTIONATION OF THE REACTANTS IS SUBSTANTIALLY AVOIDED, PASSING A VAPORIZED ENTRAINER COUNTERCURRENTLY TO THE MIXTURE THROUGH THE LIQUID REACTION MIXTURE IN THE ENTRAINER ENTRANCE ZONE AND INTO SUCCESSIVE ZONES CONTAINING SAID MIXTURE TO AN EXIT NEAR THE ENTRANCE ZONE FOR SAID ALCOHOL AND REAGENT AND WITHDRAWING THE ESTERIFIED PRODUCT FROM ONE OR MORE ZONES IN THE REGION WHERE THE ENTRAINER IS INTRODUCED. 